1. Field of the Invention
The present invention relates to a two panel projection system used in a projection type display.
2. Background of the Related Art
Two panel systems represent an attractive compromise between three panel systems and one panel systems. Three panel systems have high brightness, but also have a high component count. Single panel systems are simplest (no panel alignment, and low component count), but have reduced luminance and potential for color artifacts.
Single panel projection systems are being realized using Texas Instruments digital light processing (DLP) technology (see U.S. Pat. No. 5,612,753), which use a rotating color wheel to time sequence the primary illumination colors. Full color images are produced by sequentially projecting primary colored frames, that when viewed, are temporally integrated by the eye. The color wheel is unattractive relative to solid-state color shutters, but are used presently with the DLP technology due to its polarization insensitivity. Inexpensive single liquid crystal on silicon (LCOS) panels are beginning to be used to implement time sequential systems, which use polarized light and are well matched to liquid crystal based dynamic polarization modulation. Although these single panel systems are small and lightweight (and ultimately very inexpensive), they are intrinsically less efficient than the three panel approaches because two thirds of the light is blocked at any instant. These single panel systems also require high frame rates to avoid color breakup. Although the minimum field rate is 150-180 Hz, artifact mitigation may push field rates up by three times, or more.
Three panel systems employ architectures that split light into three spatially separate primary colored beams, which in turn illuminate three separate panels by two color splitting operations. The light emanating from the panels is then recombined and projected to form a full color image. These systems are the most common at the present time as they are very efficient and do not suffer from breakup, despite having video or sub-video refresh rates. However, the two color splitting operations required to split the light into three separate beams result in a bulky system size and a high component count, leading to higher cost and weight.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.
An object of the invention is to solve at least the above problems and/or disadvantages and to provide at least the advantages described hereinafter.
In the present invention, a two panel projection system is implemented without significantly increasing the component count over a single panel projection system. The two panel system of the present invention utilizes a single splitting/combining Polarizing Beam Splitter (PBS), where colors are encoded with polarization both dynamically and passively. The design of the present invention thus maintains the back-focal length of a single panel system, and simply places an additional panel at a port normally discarded in a single panel system. Color break-up and LCD frame-rate are reduced in the present invention relative to that of a single panel system. In a preferred embodiment, a color-balanced system is used which has a brightness much closer to a three panel system than a single panel system. The invention relates primarily, but not exclusively, to reflective liquid crystal on silicon (LCOS) micro-display technology.
In the present invention, two panel hybrid split-path sequential architectures are used. In the present invention, the problems of the one and three panel systems are present to some degree, but the extent to which these problems are observed is significantly reduced compared to either one individually, while still benefitting from aspects of the one and three panel systems. For example, the component count of the two panel system of the present invention is not significantly greater than a single panel system, and substantially less than a three panel system. The two panels each reside directly adjacent to the PBS, and therefore the two panel system has the same back-focal-length as a single panel system, which reduces projection lens cost. The frame rates necessary for good image quality can also be significantly lower than that required for the single panel system, reducing performance demands and cost of the panel. The throughput is at least the average of that obtained by the single and three panel systems, and by considering the correction to the transmitted color coordinates, the throughput of a two panel system can be surprisingly close to that of a three panel system. This is particularly so for a television projection system, where correct color balance and reduced color temperature can force significant green attenuation.
Two panel systems have been realized with DLP technology, but require using both color and input/output beam separation optical elements, thus making the overall two panel DLP optical system unattractive. The concept behind the present invention is to use a single splitting and combining element, or a Polarized Beam Splitter (PBS), with two liquid crystal panels to realize a low cost, compact, high-performance system. Retarder stack based filters or other temporal modulators in conjunction with the PBS of the present invention enable this approach.
To achieve the above objects of the present invention in whole or in parts, there is provided an apparatus that includes a first reflecting panel that receives image information for a first color, a second reflecting panel that receives image information for a second color and a third color, a temporal modulator that receives and modulates light that includes a first color light, a second color light, and a third color light, and a beamsplitting and combining element having a single reflecting/transmitting surface that reflects and transmits the first color light to the first panel and the second and third color light to the second panel and combines images reflected from the first reflecting panel and the second reflecting panel.
To further achieve the above objects of the present invention in whole or in parts, there is provided an apparatus that includes a first transmissive panel that receives image information for a first color, a second transmissive panel that receives image information for a second color and a third color, a temporal modulator that receives and modulates light that includes a first color light, a second color light, and a third color light, and a beamsplitting and combining element having two reflecting/transmitting surfaces, one for reflecting or transmitting at least the first color light to the first panel, and a second one for reflecting or transmitting the second and third color light to the second panel, the beamsplitting and combining element further combines images from the first transmissive panel and the second transmissive panel.
To further achieve the above objects of the present invention in whole or in parts, there is provided an apparatus that includes a first panel that receives image information for a first color, a second panel that receives image information for a second color and a third color, a temporal modulator and polarizer unit that receives light that includes a first color light, a second color light, and a third color light, and passes either the first color light and the second color light or the first color light and the third color light, and a single beamsplitting and combining device for directing the first color light to the first panel and the second or third color light to the second panel.
To further achieve the above objects of the present invention in whole or in parts, there is provided an apparatus that includes a first panel that receives at least a first color light and outputs a first color image, a sequential panel that sequentially receives a second color light and a third color light and sequentially outputs a second color image and a third color image, a temporal modulator that receives and modulates light that includes the first color light, the second color light and the third color light, a beamsplitter optically coupled to the temporal modulator, wherein the beamsplitter receives the light and directs at least the first color light to the first panel and the second color light and the third color light to the sequential panel, wherein the beamsplitter further sequentially outputs the second color light and the third color light to the sequential panel to yield the second color image and the third color image, and wherein the beamsplitter combines the first color image with the second color image or the third color image, wherein the first panel, the sequential panel, and the temporal modulator operate cooperatively to yield a full color image to an observer.
To further achieve the above objects of the present invention in whole or in parts, there is provided a method for projecting a full color display from a two panel system that includes directing a light beam to a temporal modulator, temporally modulating colors in the light beam, splitting the light beam into a first color light beam and a second color light beam, illuminating a first panel with at least the first color light beam, illuminating a second panel with the second or third color light beam, receiving and recombining light emitted from the illumination of the first and the second panels, and directing the recombined light through a projection lens.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objects and advantages of the invention may be realized and attained as particularly pointed out in the appended claims.